A sigma-delta converter (or delta-sigma converter) can be used to convert an analog signal to a digital signal, such as for audio, communications, measurement, or other applications. A sigma-delta analog-to-digital converter (ΣΔ ADC) includes analog and digital signal processing components. The analog components can form a sigma-delta modulator using a comparator, a switch, and one or more integrators and analog summing circuits. The digital components can include a digital signal processor, generally configured as a filter and decimator.
Delta modulation techniques can be used to generate information about a change in signal value between consecutive samples. In delta modulation, an analog signal can be quantized by a single-bit ADC circuit, for example, a comparator circuit. A digital ADC output signal can be converted to an analog signal, such as using a one-bit digital-to-analog converter (DAC) circuit.
In operation, a sigma-delta ADC circuit can receive an analog input signal that includes a signal portion from a feedback DAC circuit. The input signal can be provided to an integrator circuit, and the output of the integrator circuit can be provided to a comparator circuit. The output of the comparator circuit can be provided to the feedback DAC circuit and a digital output filter. A negative feedback loop can be established using the comparator circuit and the feedback DAC circuit. The negative feedback loop can provide an average feedback DAC circuit output voltage that is substantially equal to the analog input signal voltage. As a result, the average value of the analog input signal voltage can be encoded in the serial bit stream output from the comparator. The digital output filter can process the serial bit stream and provide the sigma-delta ADC circuit output signal.